Figure 1.
Dynamic regimes and resulting signal intensities from PT ssNMR experiments.
Theoretical 1H to 13C polarization transfer efficiency as a function of correlation time τc and order parameter |SCH| for a CH2 segment at the magnetic field 11.74 T and the magic-angle spinning frequency 5 kHz, calculated with input parameters equal to the present experimental settings (see Solid-state NMR). The map is color-coded according to the calculated intensities of the INEPT (red) and CP (blue) polarization transfer schemes. White represents inefficient polarization transfer for both INEPT and CP. Typical values of τc and SCH, in the different dynamic regimes, and the expected intensities for the INEPT and CP polarization transfer schemes, are listed to the right of the figure. Adopted from ref. [14].
Figure 2.
Peak assignment of molecular segments in the SC.
13C DP MAS NMR spectra of (A) intact SC, (B) isolated corneocytes, and (C) SC model lipids at 60°C. The schematics illustrate SC with corneocytes filled with keratin filaments, surrounded by a multilamellar lipid matrix. Peaks originating from the keratin and the lipids are assigned in (B) and (C), respectively, following the IUPAC nomenclature. For peaks assigned to several amino acid residues, the names are ordered according to the expected abundance. Spectra A and B are scaled to equal intensity at 172.8 ppm, while spectra A and C are scaled to give equal intensity at 30.4–30.6 ppm. See Figure S1 (E) for standard numbering of cholesterol carbons and labels of lipid carbons.
Figure 3.
Water affects the molecular mobility of the SC components.
13C MAS NMR spectra of intact SC as a function of RH (water content) at 32°C using DP (grey), CP (blue), and INEPT (red) pulse sequences for preferential enhancement of the signals from molecular segments in either rigid (CP) or mobile (INEPT) microenvironments. Prominent resonance lines from keratin (Leu Cβ, Lys Cε, Gly Cα, Ser Cα, Ser Cβ) and lipids (all-trans and trans/gauche (CH2)n, (ω−1)CH2, ωCH3) are labeled in the data obtained at 50 wt% water. The dots in the 30 wt% water spectra indicate peaks of cholesterol (C12/24, C4, C14/17 and C9, cf., Fig. 2 C).
Figure 4.
Heating affects the SC molecular mobility differently than hydration.
13C MAS NMR spectra of intact SC as a function of temperature and water content using DP (grey), CP (blue), and INEPT (red) pulse sequences. The schematics illustrate the dynamic state of the SC components by color coding according to the observed INEPT (red, mobile) and CP (blue, rigid) intensities of the signature peaks for lipids (all-trans and trans/gauche (CH2)n, (ω−1)CH2, ωCH3), as well as the keratin core (Cα-region centered around 57 ppm, Leu Cβ, Lys Cε) and the protruding terminals of the keratin filaments (Gly Cα, Ser Cα, Ser Cβ).